Automotive internal combustion engines are known to be coupled to transmissions through hydrodynamic converters which provide torque multiplication and hydrodynamic damping benefits. Hydrodynamic converters, also commonly referred to as torque converters, include a driving member or pump coupled to an engine output shaft and a driven member or turbine coupled to a transmission input shaft. A hydraulic coupling is provided between the driving and driven members. The torque multiplication and damping characteristic of the torque converter varies with the slip between the driving and driven members which is defined as the difference in rotational speed between the two members. In a torque multiplication region of torque converter operation, the slip is relatively high. In a coupling region of torque converter operation, slip is relatively low. The region of operation of the torque converter is dictated by engine operating conditions, and may be difficult to predict under transient operating conditions. Accordingly, torque converter slip may be difficult to predict under transient operating conditions.
More specifically, while the rate of rotation of the torque converter driving member, which is coupled to the engine output shaft, may be known, and while the rate of rotation of the transmission output shaft may be known using conventional sensor mechanizations, the transmission input shaft speed is not known with precision during certain transient operating conditions. This lack of precision can lead to reduced powertrain transient control precision and reduced powertrain diagnostic coverage.
Transmission input shaft speed sensors are known to be coupled to an automotive vehicle drivetrain to transduce the rate of rotation of the input shaft of the transmission into a signal applied for powertrain control and diagnostics. Such sensors provide transmission input shaft rate of rotation information which, when coupled with other available information, indicate slip across the torque converter. However, such sensors and their corresponding wiring and circuitry add significantly to the cost and complexity of powertrain control and diagnostics. Typically such sensors take the form of Hall effect, variable reluctance, or magnetoresistive transducers positioned adjacent a series of teeth or notches machined into or coupled to the transmission input shaft for transducing passage of the teeth or notches by the transducer into a predictable change in a transducer output signal. The output signal is sampled by analog to digital conversion circuitry which outputs a digital representation of the transducer output for use by a digital control in carrying out control and diagnostics operations.
It would be desirable to provide accurate torque converter slip information for use in powertrain control and diagnostics without the substantial cost and complexity associated with use of conventional transmission input shaft speed transducers.